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<p>Laser-directed energy deposition (L-DED) has been widely applied in aerospace, mechanical equipment manufacturing, and component repair. However, defects such as pores still limit the forming quality of L-DED-fabricated components. In this study, a numerical model considering pre-placed Ti6Al4V powder particles and pores was established based on the level-set method to investigate the effect of defocus distance on droplet–melt pool interaction and pore evolution during the L-DED process of Ti6Al4V alloy. A pulsed Nd:YAG laser was used in the experiments, with a laser power of 1600W, a scanning speed of 7.5mm/s, and defocus distances ranging from −2 to 2mm. The simulation results indicate that high-energy droplets under positive defocus conditions can enhance melt pool flow and promote bubble escape, reducing the bubble escape time to 27.4ms. The experimental results show that the porosities of the samples at defocus distances of 2 mm, 1 mm, 0 mm, −1 mm, and −2 mm were 0.056%, 0.052%, 0.250%, 0.266%, and 0.288%, respectively, with the lowest porosity obtained at a positive defocus distance of 1mm. These results demonstrate that an appropriate positive defocus distance is beneficial for promoting bubble escape and reducing the internal porosity of Ti6Al4V alloy components fabricated by L-DED.</p>

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Mechanism of defocus distance affecting molten pool dynamics in laser-directed energy deposition process

  • 期刊论文

  • 发表日期：

    2026年7月2日

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  • Hao-Yuan Chen,
  • Jin-Long Meng,
  • Hong Yin,
  • Chun-Tang Liu,
  • Ming Li,
  • Hong-Wei Hu,
  • Wei Han,
  • Sheng-Nan Shen,
  • Xue-Chun Wang,
  • Qian-Xing Yin

摘要

Laser-directed energy deposition (L-DED) has been widely applied in aerospace, mechanical equipment manufacturing, and component repair. However, defects such as pores still limit the forming quality of L-DED-fabricated components. In this study, a numerical model considering pre-placed Ti6Al4V powder particles and pores was established based on the level-set method to investigate the effect of defocus distance on droplet–melt pool interaction and pore evolution during the L-DED process of Ti6Al4V alloy. A pulsed Nd:YAG laser was used in the experiments, with a laser power of 1600W, a scanning speed of 7.5mm/s, and defocus distances ranging from −2 to 2mm. The simulation results indicate that high-energy droplets under positive defocus conditions can enhance melt pool flow and promote bubble escape, reducing the bubble escape time to 27.4ms. The experimental results show that the porosities of the samples at defocus distances of 2 mm, 1 mm, 0 mm, −1 mm, and −2 mm were 0.056%, 0.052%, 0.250%, 0.266%, and 0.288%, respectively, with the lowest porosity obtained at a positive defocus distance of 1mm. These results demonstrate that an appropriate positive defocus distance is beneficial for promoting bubble escape and reducing the internal porosity of Ti6Al4V alloy components fabricated by L-DED.